image/jpeg: ignore an incorrect but harmless trailing restart marker.

Fixes #4084.

R=r
CC=golang-dev
https://golang.org/cl/6526043

diff --git a/src/pkg/image/jpeg/reader.go b/src/pkg/image/jpeg/reader.go
index 652dc5f6b5f1409db047504d415e5e1c676c49b5..5ed142a6c6b3ea622186eb9d2648b88d1e4d65cd 100644 (file)
--- a/src/pkg/image/jpeg/reader.go
+++ b/src/pkg/image/jpeg/reader.go
@@ -403,6 +403,15 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
                if marker == eoiMarker { // End Of Image.
                        break
                }
+               if rst0Marker <= marker && marker <= rst7Marker {
+                       // Figures B.2 and B.16 of the specification suggest that restart markers should
+                       // only occur between Entropy Coded Segments and not after the final ECS.
+                       // However, some encoders may generate incorrect JPEGs with a final restart
+                       // marker. That restart marker will be seen here instead of inside the processSOS
+                       // method, and is ignored as a harmless error. Restart markers have no extra data,
+                       // so we check for this before we read the 16-bit length of the segment.
+                       continue
+               }
 
                // Read the 16-bit length of the segment. The value includes the 2 bytes for the
                // length itself, so we subtract 2 to get the number of remaining bytes.
@@ -431,7 +440,7 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
                        err = d.processSOS(n)
                case marker == driMarker: // Define Restart Interval.
                        err = d.processDRI(n)
-               case marker >= app0Marker && marker <= app15Marker || marker == comMarker: // APPlication specific, or COMment.
+               case app0Marker <= marker && marker <= app15Marker || marker == comMarker: // APPlication specific, or COMment.
                        err = d.ignore(n)
                default:
                        err = UnsupportedError("unknown marker")